Solar heating systems conventionally are composed of solar collectors, a thermal storage unit and heat using apparatus. A heat transfer medium such as fluid, gas or air is usually circulated through the solar collectors and the heat thus gained by the material is deposited in the storage medium.
Storage media such as water tanks, dry stones and the like have conventionally been used.
In systems using hot air alone, cold return air from the building is circulated through solar panels which are exposed to sunlight. Blackened surface in the solar panels convert the solar energy into increases in ambient air temperature within the solar panels. The heated air is then circulated either to the structure to be heated or to a storage medium such as stones. During insufficient insolation to maintain the temperature of the structure at the desired level, the air from the building is circulated through the heated stones to warm it in order to overcome the temporary deficit.
In water systems, plain water may be circulated through the solar collectors and into a storage tank to heat the water resident in the storage tank. Upon demand, the heated water is drawn from the storage tank and is circulated through radiators in the building to elevate the building temperature. This system suffers from the drawback that water without anti-freeze is unsuitable in climates in which freezing can occur. Consequently, the thermal collection and thermal storage and distribution are typically separated. Thus, the solar collectors may use a non-freezing medium such as a water-glycol mixture and the heat gathered by the solar collectors deposited in a water storage tank using a heat exchanger.